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Yes - "There are two blocks, one with two-bolt mains and one with four-bolt mains. They both have the same 10125327 casting number, so there’s no sure way to know which one you have until you get the pan off. However, if it came out of a Corvette, it should be a four-bolt block, and if it came out of anything else, it was supposed to be a two-bolt. GM used the two-bolt block for everything but the Corvette because it had plenty of strength and it weighed a little bit less".
2001 White/Black/Black Vert M6/Z51: LPE TT650 580rwhp/540rwtq
1994 White/Red M6 LT1 Corvette: 374rwhp/345rwtq,12.37@119: Heads/Cam/4.10's
2001 Ford Lightning: 425rwhp/503rwtq,12.85@108
2006 Cobalt LS (DD)
My guess is that in the manufacturing process, the exact same mold is used for the 2 bolt vs. 4 bolt blocks. The block itself is the same core part. The "327" is part of the mold. I think it is a machining process that makes the difference for the 2 bolt cap and 4 bolt cap. That would explain why you can't ID the "block" itself, because they are essentially the same cast part.
'93 Quasar Blue 6-speed, lowered, VBP sport springs, Z07 bars, RD camber brace, poly bushings, polished A-arms, 11" Chrome ZR1's, C5 brakes, tint, 14k miles